Two consecutive lectures of any subject at a specific day

[TAHIR]

A subject have 6 lectures in 4 days , how we fix two consecutive lectures in a specific day?

[Volker Dirr]

use an activity that is split into 2+2+1+1 with 100% weight.
Then there are a lof of different preferred time constraint possible.
Impossible to say witch one is the "best" in your case, since I don't know your data set.
maybe us constraint prefered time slots for subactivities with duration 2.

[TAHIR]

What is meant by component number (split index) ?
Time constraint subactivities preferred time slots.

And what is difference between constraints "preferred starting time and preferred time slots?

[Volker Dirr]

Let's assume you have got an activity split into 1+1+1+1.
So there are 4 sub activities.
If you add a constraint with "component number 1", then this constraint will only affect the first sub activity, but not the 3 other ones.

About the second question: If you have only activities with duration 1, then there is no difference.
If you have activities with duration 2, then there is a difference.

For example: You allow only the first hour. All other hours are not allowed.
If you do that with "preferred time slots", then it is impossible to place an activity with duration 2.
If you do the same with "preferred starting times", then it is allowed to place activities with duration 2 (or more) in the first hour.